ab08960f64
Change pushcli / popcli so that they can never turn on interrupts unexpectedly. That is, if interrupts are on, then pushcli(); popcli(); turns them off and back on, but if they are off to begin with, then pushcli(); popcli(); is a no-op. I think our fundamental mistake was having a primitive (release and then popcli nee spllo) that could turn interrupts on at unexpected moments instead of being explicit about when we want to start allowing interrupts. With the new semantics, all the manual fiddling of ncli to force interrupts off in certain sections goes away. In return, we must explicitly mark the places where we want to enable interrupts unconditionally, by calling sti(). There is only one: inside the scheduler loop.
70 lines
2.3 KiB
C
70 lines
2.3 KiB
C
// Segments in proc->gdt
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#define SEG_KCODE 1 // kernel code
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#define SEG_KDATA 2 // kernel data+stack
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#define SEG_UCODE 3
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#define SEG_UDATA 4
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#define SEG_TSS 5 // this process's task state
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#define NSEGS 6
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// Saved registers for kernel context switches.
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// Don't need to save all the %fs etc. segment registers,
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// because they are constant across kernel contexts.
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// Save all the regular registers so we don't need to care
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// which are caller save, but not the return register %eax.
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// (Not saving %eax just simplifies the switching code.)
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// The layout of context must match code in swtch.S.
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struct context {
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int eip;
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int esp;
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int ebx;
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int ecx;
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int edx;
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int esi;
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int edi;
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int ebp;
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};
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enum proc_state { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };
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// Per-process state
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struct proc {
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char *mem; // Start of process memory (kernel address)
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uint sz; // Size of process memory (bytes)
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char *kstack; // Bottom of kernel stack for this process
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enum proc_state state; // Process state
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int pid; // Process ID
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struct proc *parent; // Parent process
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void *chan; // If non-zero, sleeping on chan
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int killed; // If non-zero, have been killed
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struct file *ofile[NOFILE]; // Open files
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struct inode *cwd; // Current directory
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struct context context; // Switch here to run process
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struct trapframe *tf; // Trap frame for current interrupt
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char name[16]; // Process name (debugging)
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};
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// Process memory is laid out contiguously, low addresses first:
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// text
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// original data and bss
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// fixed-size stack
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// expandable heap
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// Per-CPU state
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struct cpu {
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uchar apicid; // Local APIC ID
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struct proc *curproc; // Process currently running.
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struct context context; // Switch here to enter scheduler
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struct taskstate ts; // Used by x86 to find stack for interrupt
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struct segdesc gdt[NSEGS]; // x86 global descriptor table
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volatile int booted; // Has the CPU started?
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int ncli; // Depth of pushcli nesting.
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int intena; // Were interrupts enabled before pushcli?
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};
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extern struct cpu cpus[NCPU];
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extern int ncpu;
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// "cp" is a short alias for curproc().
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// It gets used enough to make this worthwhile.
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#define cp curproc()
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